#1 3 5 7 9……

def fac(k):
    i = 2
    t = 1
    while i <= k:
        t *= i
        i += 1
    return t
def sum(n):
    s = 0
    i = 1
    while i <= n:
        s = s + fac(i)
        i += 2
    return s
print(sum(20))